Morphology and immuno‐histochemistry of the caudal neurosecretory system of a marine euryhaline fish,dicentrarchus labrax, acclimated to low salinity

Abstract

The morphology and the immunohistochemistry of the caudal neurosecretory system of Dicentrarchus labrax were analysed after the fish acclimatation to fresh water. Two different sized neurosecretory cells have been identified in seawater-acclimated fish and denoted as anterior and posterior cells. The two types of cells share similar patterns and intensities of immunoreactivity with urotensin I and urotensin II antisera. Posterior neurosecretory cells decreased in size in freshwater-acclimated specimens, whereas anterior cells did not show changes. Urophyses of seawater-and freshwateracclimated fish reacted with both antisera. Immunohistochemistry of the urophysis did not provide evidence for a significant difference in the activity of the caudal neurosecretory system between seawater-and freshwater-acclimated fish. However, on a morphological basis it was possible to suggest that the caudal neurosecretory system of the sea bass is involved in the hyperosmoregulation.

Caudal neurosecretory system of the zebrafish: ultrastructural organization and immunocytochemical detection of urotensins

“…With respect to the ultrastructural data, our observations are in agreement with the general features of the submicroscopical organization of the caudal neurosecretory system as established previously for other species of fresh or seawater teleost fishes (Enami 1959;Bern and Takasugi 1962;Oota 1963;Sano et al 1966;Fridberg and Bern 1968;Vigh-Teichmann and Vigh 1979;Kriebel 1980;Yulis and Lederis 1986;Cioni et al 1996Cioni et al , 1998. Thus, here we merely comment on some peculiarities of the zebrafish.…”

“…This means that a certain amount of neurosecretion might be released directly into the cerebrospinal fluid as previously suggested by Vigh-Teichmann et al (1976) and Yulis and Lederis (1986) in the sucker spinal cord. Likewise Cioni et al (1996) have described UII cells contacting the cerebrospinal fluid in Dicentrarchus labrax. Another type of secretory structure (Fig.…”

Nitric Oxide and the Neuroendocrine Control of the Osmotic Stress Response in Teleosts

“…For instance, immunoreactive cells for both urotensins are fewer than UII-ir cells in goldfish. Moreover, a majority of UII-ir cells were observed in the CNSS of the European sea bass [176] and comparable results were obtained in zebrafish by double- UI/UII immunolabeling [167]. On the contrary, most Dahlgren cells were UI-ir in flounder whereas few cells immunoreacted for both UI and UII [141,177].…”

“…Old literature data was conflicting about the effects of environmental salinity on the CNSS morphology and ultrastructure [176,185,186,187,188,189], the aminoacid uptake [190], the innervation [191] and the pattern of UI/UII immunoreactivity of caudal neurons and/or the urophysis. Some data indicated an increase in UI- and/or UII-ir in the Dahlgren cells and the urophysis of fish transferred to low-salinity in comparison to SW-adapted fish [192,193].…”

Morphology and immunohistochemistry of the caudal neurosecretory system in tetraodontids

“…There is evidence for an osmoregulatory role of urotensins, both direct and indirect (Lederis et al, 1985a;Bern, 1990). In addition, there is considerable evidence concerning the effects of water salinity changes on the morphology, the ultrastructure (Takasugi & Bern, 1962;Fridberg et al, 1966;Chevalier, 1976;Kriebel, 1980;Sacks & Chevalier, 1984;Cioni et al, 1996), the aminoacid uptake (Chevalier, 1978), the innervation (Audet & Chevalier, 1981), and the pattern of UI/UII immunoreactivity of the caudal neurosecretory neurons and the urophysis (Owada et al, 1985;Minniti et al, 1989;Arnold-Reed et al, 1991;Larson & Madani, 199D-The bulk of data indicates that CNSS plays a major role in the control of body fluid homeostasis and osmoregulation.…”